1. Field of the Invention
The present invention relates to a zoom lens and image capture apparatus. More specifically, the present invention relates to a zoom lens that provides a higher performance and a higher zoom ratio while having a small size, as well as to an image capture apparatus equipped with such a zoom lens.
2. Description of Related Art
In recent years, small-size image capture apparatuses such as consumer video cameras and digital video cameras have been wide spread for household use. For the small-size image capture apparatuses of this type, portability is taken into serious consideration. Miniaturization is always desired as well as a higher image quality. For that reason, with respect to image-capturing lenses, particularly zoom lenses respectively mounted in the small-size image capture apparatuses, there is a need for a smaller size as well as enhancement of lens performances. The smaller size may be achieved, for example, by reducing an overall length and/or width. Further, there is also a great recent demand for a higher zoom ratio. It becomes more difficult to find appropriate designs adaptable to meet such demands for the miniaturization, the higher image quality and the higher zoom ratio.
Such being the case, in Japanese Patent Application Publication No. JP 2000-89111 (hereinbelow, referred to as Patent Document 1), for instance, a zoom lens is disclosed, which includes, in order and from the side of an object, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power and a fifth lens group having a refractive power approximately close to nil. The third lens group is configured with a cemented lens of a convex lens and a concave lens, and the fifth lens group is configured with a cemented lens of a concave lens and a convex lens. Use of a lens configuration of this type allows to achieve a optical zoom ratio as high as ten times.
In Japanese Patent Application Publication No. JP 2001-33694 (hereinbelow, referred to as Patent Document 2), a zoom lens of a different type is disclosed, which includes, in order and from the side of an object, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a positive refractive power. The fifth lens group is configured so as to have a lens surface that is in a spherical or plane shape. Use of a lens configuration of this type allows to achieve a optical zoom ratio as high as twenty-five times.